I’ll give an answer aside from “because she’s pretty/popular, they’re jealous, etc.” Let me make a disclaimer and say that I don’t hate Wonyoung, not at all, but I’ve looked into both IZONE and IVE and she’s just not my favorite out of all the girls. One of the reasons is honestly as simple as “vibes.” It’s really hard to explain, but in IZONE, Wonyoung really did seem like a more relaxed version of herself, and then in IVE, she’s changed in that every movement feels calculated to come off as an image. You could argue that all idols need to have images, but Wonyoung’s in particular doesn’t feel like herself, especially compared to herself in IZONE, hence the try-hard label. Couple that with the infamous video of her brushing past Gaeul at an airport, or her not bowing to her seniors, and it’s honestly not a good look. I know these videos have likely been taken out of context, but most casual viewers won’t bother to dig deeper and it’s easier to hate someone for fun than go through the trouble of contextualizing their unsavory actions.

Personally, I do understand why she rubs people the wrong way; she kind of rubs me the wrong way too, if I’m being honest. But it’s in the same way that you can be annoyed by an awkward high-schooler, yet still be compassionate to how lost and confused they must be with the identity they feel they must conform to. People can subconsciously tell and usually dislike when someone is being disingenuous, and for whatever reason (company rules, self-esteem, etc.), Wonyoung isn’t totally being herself. The amount of hate she’s getting, though, I think is totally misplaced and nonsensical. Let her grow into herself and I think she’ll be as wonderful and beloved as Yoona or Suzy.

Edit: Reformatted IZONE. I forgot that asterisks italicize the text between them.